Joseph Gordon-Levitt is siding with Mayor Bloomberg about adding more bike lanes in the city. “I think it’s great for the city to support bike riding — and the more bikes and the fewer cars in the city, the better it will be,” he told us during a screening of “Premium Rush,” at Regal Union Square. Gordon- Levitt, who plays a bike messenger, isn’t quitting his day job. “Two years ago, when we were shooting this, I was in better shape, I could probably hang. I couldn’t do it right now. ”